Abstract:
Digital Q3 Flood Data are developed by scanning the existing FIRM hardcopy, vectorizing a thematic overlay of flood risks. Vector Q3 Flood Data files contain only certain features from the existing FIRM hardcopy. Q3 vector data are contained in one single countywide file, including all incorporated and unincorporated areas of a county.

Digital Q3 Flood Data do ... not replace the existing FIRM hardcopy or, if one exists, DFIRM product. The product is designed to support planning activities, some Community Rating System activities, insurance marketing, and mortgage portfolio reviews. It does not provide base flood elevation information; thus, it has limited application for engineering analysis, particularly for site design or rating flood insurance policies for properties located within Special Flood Hazard Areas (SFHAs).

Digital Q3 Flood Data are not tied to a base map, are not used to produce a new version of the FIRM hardcopy, and are not subjected to community review. The digital Q3 Flood Data are designed to provide guidance and a general proximity of the location of Special Flood Hazard Areas.

The digital Q3 Flood Data product can be a valuable tool in screening property addresses within a Geographic Information System to determine flood risks. However, since the geographic processing performed to develop digital Q3 Flood Data may introduce differences with the FIRM hardcopy source, users must apply considerable care and judgment in the application of this product. For instance, digital Q3 Flood Data may be overlaid on highly detailed large-scale community base mapping data, but, if parcel level determinations are made, they must be prefaced with information about the accuracy of the data from which they are derived.

Quality
Edge-matching errors, overlaps and underlaps in coverage, and similar problems are not corrected during digitizing or scanning and vectorizing the Q3 Flood Data. Although FEMA has established no independent quality control/quality assurance program for the Q3 Flood Data, the Q3 Flood Data files are distributed only after they have passed checking routines contained in FEMA's Q3QA Checking Software. The data are accompanied by documentation showing that the files have been evaluated and passed. FEMA has established a User Support mechanism through which any problems found with the data can be identified and channeled back to FEMA for resolution.